Folding Array

http://www.lintcode.com/zh-cn/problem/folding-array/

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Solution {
    /*
     * @param : the original array
     * @param : the direction each time
     * @return: the final folded array 
     */
    public int[] folding(int[] nums, int[] req) {
        // write your code here
        int factor = 0;
        for (int i = 0; i < req.length; i++) {
            if (i == 0) {
                factor = 1;
            } else {
                factor = 2 * factor;
            }
            if (req[i] == 0) {
                nums = left2Right(nums, factor);
            } else {
                nums = right2Left(nums, factor);
            }
        }
        return nums;
    }

    //    右半边逆序在前，左半边不动在后
    private int[] right2Left(int[] nums, int factor) {
        int length = nums.length / factor;
        List list = new ArrayList<>();
        List rightList = new ArrayList<>();
        for (int i = 0; i < factor; i++) {
            for (int j = 0; j < length; j++) {
                if (j < length / 2) {
                    list.add(nums[length * i + j]);
                } else {
                    rightList.add(nums[length * i + j]);
                }
            }
        }
        Collections.reverse(rightList);
        int[] res = new int[nums.length];
        for (int i = 0; i < res.length; i++) {
            if (i < res.length / 2) {
                res[i] = rightList.get(i);
            } else {
                res[i] = list.get(i - res.length / 2);
            }
        }
        return res;
    }


    //    左半边逆序在前，右半边不动在后
    private int[] left2Right(int[] nums, int factor) {
        int length = nums.length / factor;
        List list = new ArrayList<>();
        List rightList = new ArrayList<>();
        for (int i = 0; i < factor; i++) {
            for (int j = 0; j < length; j++) {
                if (j < length / 2) {
                    list.add(nums[length * i + j]);
                } else {
                    rightList.add(nums[length * i + j]);
                }
            }
        }
        Collections.reverse(list);
        int[] res = new int[nums.length];
        for (int i = 0; i < res.length; i++) {
            if (i < res.length / 2) {
                res[i] = list.get(i);
            } else {
                res[i] = rightList.get(i - res.length / 2);
            }
        }
        return res;
    }
}